The present invention relates to a circuit arrangement for the generation of I,Q waveforms. I,Q waveforms (In-phase/Quadrature, i.e. in phase and 90 degrees phase-shifted) are multiplied, for example, into the sin and cos signal forms of a transmission-frequency signal, whereafter the obtained signals are summed. The signal thus obtained is a frequency-modulated signal, for example, a radio-frequency transmission signal. The modulating signals may be analog or digital signals.
The generation of I,Q waveforms from an analog signal is known, for example, from Finnish patent application No. 843 826. The circuitry type represented in that application is shown in the form of a block diagram in FIG. 1. In it, a voltage age X(t), i.e. dx(t)/dt, corresponding to the incoming signal, is used for controlling a voltage-controlled oscillator 1, the average frequency f.sub.o of which is low compared with the transmission frequency, for example in the order of 100 kHz. The oscillator 1 output EQU U=cos [.omega..sub.o t+k . x(t)],
which includes frequency modulation, is divided into two branches, which are multiplied by the sin and cos signal forms of an f.sub.o -frequency signal. This f.sub.o -frequency signal is unmodulated. The multiples of f.sub.o, which are created as a product of mixing, are filtered out of the signals of both branches by means of low-pass filters 4, whereupon the desired sin and cos signal forms are obtained as the result.